The present invention relates to the art of grinding in general, and more particularly to improvements in methods and machines for grinding rotary workpieces. Still more particularly, the invention relates to improvements in a method of and in a (circular or surface) grinding machine for removing material from the peripheral or internal surfaces of rotating workpieces.
It is known to equip a surface grinding machine with automatic work inserting and removing means and with means for at least intermittently monitoring the diameter and/or other dimensions of the workpiece at the grinding station so as to allow for immediate changes in the mode of operation if the monitored dimension or dimensions deviates or deviate from a desired or optimum value. It is also known to provide a surface grinding machine with means for ascertaining the condition and the accuracy of the monitoring means so as to avoid the making of longer or shorter series of ultimate products whose dimensions deviate from a desired value. As a rule, the monitoring means (e.g., a standard measuring head with two or more work-contacting sensors) is calibrated with a pattern which is a replica of a finished workpiece and whose dimensions match the desired or optimum values. Signals which are generated by the monitoring means during scanning of a workpiece as well as during scanning of a pattern are transmitted to the control circuit of the grinding machine for evaluation and for the carrying out of adjustments, if necessary. The aforedescribed mode of operation can be relied upon irrespective of whether the machine employs one or more grinding tools.
Continuous monitoring of workpieces during removal of material therefrom in a grinding machine is desirable and advantageous if the workpieces are to be treated with a high or extremely high degree of precision. For example, such workpieces can constitute camshafts for use in internal combustion engines or for other purposes. Frequent monitoring of the dimensions of workpieces during removal of material is particularly important and desirable when the grinding machine is set up to turn out long series of identical workpieces, i.e., when the intervals for changes of setup are infrequent and the machine could turn out large numbers of defective products including rejects during an interval between stops which take place for the purpose of allowing a changeover to treatment of different types of workpieces. Presently known numerical and other automatic ontrols of a modern high-speed surface grinding machine are capable of immediately evaluating the signals which are generated by the monitoring means and of immediately adjusting the machine if the monitored dimensions of a workpiece deviate from standard or optimum dimensions.
The sensors which are used in a measuring head to ascertain the dimensions of a workpiece at the grinding station are subjected to extensive wear since they come into contact with a rotating part which is in the process of being treated by one or more grinding wheels. The accuracy of measurement decreases with progressing wear upon the sensors so that, in the absence of any remedial action, the machine could turn out large numbers of defective products. This is the reason for the utilization of the aforediscussed pattern which is contacted by the sensors from time to time in order to ascertain whether or not the sensors are still capable of furnishing accurate signals such as are required in the course of a particular type of grinding operation.
German Offenlegungsschrift No. 31 36 443 discloses a method of and an apparatus for zero setting the measuring head in a circular grinding machine. The grinding machine which is disclosed in this German printed publication comprises a measuring head which is pivotable into engagement with a measuring pin mounted on the machine within the range of movements of the measuring head. Signals which are generated in response to engagement between the measuring head and the measuring pin are used to effect a zero setting for (i.e., to select the starting position of) the measuring head. The just discussed machine exhibits the drawback that the measuring pin cannot be placed at a substantial distance from the grinding station, i.e., it must be located within the range of the sensors of the measuring head. Therefore, the pin is frequently in the way and adversely affects the accessibility of the measuring station. Moreover, the measuring pin is located in the space for sprays of water which is caused to cool the workpiece during removal of material by one or more grinding wheels. The liquid medium carries particulate and other contaminants which deposit and incrustate on the measuring pin and thus affect the accuracy of adjustment of the measuring head when the latter is caused to place its sensors into contact with the thus contaminated measuring pin.